Fundamental characteristics required for electrophotographic light-sensitive materials include (1) the ability to carry out electrification in the dark so as to have a suitable electric potential, (2) the disappearance of electric charges in the dark is small and (3) the electric charges can be rapidly removed by exposing to light.
Hitherto, as photoconductive materials for electrophotographic light-sensitive materials, inorganic substances such as selenium, cadmium sulfide or zinc oxide, etc. have been used.
However, these inorganic substances have various disadvantages. For example, selenium which is currently widely used, satisfies the above-described requirements (1)-(3), but its production requires severe conditions which increase the cost of production, it is difficult to work so as to have a belt-shape because of its poor flexibility, and it is necessary to pay attention to handling because it is sensitive to heat or mechanical impact. Cadmium sulfide and zinc oxide have been used as light-sensitive materials by dispersing in a binder resin. However, they can not be repeatedly used in such a state because they have mechanical poor properties such as smoothness, hardness, tensile strength and friction rsistance, etc.
In recent years, for the purpose of overcoming these disadvantages of inorganic substances, electrophotographic light-sensitive materials using various organic substances have been proposed and some of them have been put into practical use.
However, with organic electrophotographic light-sensitive materials, although the mechanical characteristics and flexibility are improved to some extent, the requirements for electrophotographic light-sensitive materials have not been sufficiently satisfied because they have generally low light sensitivity and are not suitable for repeated use.
The photoconductive process for electrophotographic light-sensitive materials consists of (1) a step of generating electric charges by exposing to light, and (2) a step of transporting electric charges.
As an example of conducting steps (1) and (2) with the same substance, there is a selenium light-sensitive plate. On the other hand, as an example of conducting steps (1) and (2) with different substances, a combination of amorphous selenium and poly-N-vinyl carbazole has been well known. Function separating of electrophotographic light-sensitive materials in which steps (1) and (2) are conducted with different substances have advantages in that the scope of selection of materials to be used for the light-sensitive materials is expanded and, consequently, the electrophotographic characteristics such as sensitivity or receiving electric potential, etc. of the electrophotographic light-sensitive materials are improved. Further, substances advantageous for producing an electrophotographic light-sensitive coating film can be selected from a wide scope.
With respect to such function separating of electrophotographic light-sensitive materials, the proposals to date have not provided satisfactory results.